First thought would be that they have some sort of developmental disorder. Quickly following that thought would be the consideration that maybe they have a weird kink that they are deciding to share with this unsuspecting grocery store.

But if the person seemed happy, confident, intelligent, and attractive, and the outfit was clean, well put together, and excellently tailored, I would assume they are some kind of artist/fashion model making a statement. But still, it would be a transgressive statement.